1. Field of the Invention
The present invention relates to an oscillatory signal output circuit generating an oscillatory signal.
2. Description of the Background Art
A conventional oscillatory signal output circuit, especially a crystal oscillator circuit, includes an amplifier for amplifying a small-amplitude waveform generated by a quartz oscillator device, or crystal resonator, to output a resultant large-amplitude waveform in the form of sinusoidal wave. For example, an oscillatory signal generated as a sine wave by the amplifier is converted by an output circuit to a rectangular wave, which is outputted for use in an LSI (Large-Scale Integrated circuit), etc., as an operational clock.
An example of oscillatory circuit suitable for fabrication as an LSI and stably operable at low-voltage power supply, specifically 1.0V-1.5V, with its electric power consumption reduced is disclosed by Japanese Patent Laid-Open Publication No. 097732/1994.
However, a reduction of the electric power consumption of an oscillatory circuit needs to reduce the electric power consumption of the amplifier per se. That may cause the amplitude of an output signal from the amplifier to decrease so that variation in threshold voltage of the transistor of an output section of the oscillatory circuit driven by the output signal may prevent the output signal from going over the threshold voltage, thus causing a failure that the transistor is inoperable to the extent that no signal is outputted from the output section. In the context, the word “transistor” means at least one of a P-type and an N-type field effect transistor.